When first ________ to the market, these products enjoyed great success．
A.introducingB.introducedC.introduceD.being introduced在线课程B
解析：
考查状语从句的省略形式。句意为“这些产品刚投放市场时就很成功(销售很好)”。状语从句恢复完整时，应是“when these products were first introduced to the market”。当状语从句的主语和主句主语相一致且谓语包含动词be的某种形式时，可省略从句的主语以及动词be。本从句的主语these products和were省略后，就和题干的状语一样。故正确答案为B。